Conventional collecting and condensing designs for electromagnetic radiation emphasize collecting and redirecting the maximum amount of light from a source of radiation, approximated by a point source. To produce a small spot size based on these designs results in a decrease in radiation flux because conventional designs (i.e., the collection and redirection of the maximum amount of light) inherently conflict with the goal of concentrating the radiation flux into the smallest possible spot size when the radiation originates from conventional incoherent sources. Thus, images of small spot size may be obtained only by a corresponding decrease in flux density.
There are two basic optical designs in common use for collecting and condensing radiation. The first is a system of condenser lenses such as illustrated in FIG. 1. Condenser lenses have several problems which include creation of chromatic and spherical aberrations, relatively high cost, inherently difficult alignment, and large amount of space. Ellipsoidal reflectors as shown in FIG. 2 are also used in prior art systems. Their problems also include high cost and an unavoidable magnification of the image (i.e. a reduction in the flux density). Both of these systems tend to emphasize redirection of the maximum amount of flux from a point source at the expense of the flux density, as discussed above.
U.S. Pat. No. 4,757,431, the embodiment of which is incorporated herein by reference (FIG. 3), describes an improved condensing and collecting system employing an off-axis spherical concave reflector which enhances the maximum flux illuminating a small target and the amount of collectable flux density by a small target. The off-axis spherical concave reflector described in this patent has certain disadvantages, namely, astigmatism parallel to the direction of the off-axis displacement and the physical limitations inherent in the requirement to minimize this distance. The effect of astigmatism is to decrease the concentrating efficiency of the system and thereby reduce the flux collected at a target. The requirement to minimize the off-axis distance between the source and the target (i.e. minimize astigmatic distortion), imposes limitations on the physical dimensions of a source and target of the described embodiment. The teachings of the use of a deformable spherical concave reflector does not lead to the use of a toroidal reflector having two perpendicular and unequal radii of curvature.